1. Field of the Invention
The present invention relates to a wireless communication apparatus which is suitably adapted to a mobile station in a mobile radio communication system introducing the W-CDMA (UTRA-FDD) communication system.
2. Description of the Related Art
Standardization of the W-CDMA (UTRA-FDD) system which is one of the 3rd generation mobile communication systems is now continued by the 3GPP (3rd Generation Partnership Project). As one of the themes of standardization, the HSDPA (High Speed Downlink Packet Access) which can provide the maximum transmission rate of about 14 Mbps in the downlink is regulated.
The HSDPA introduces the adaptive modulation and coding scheme (AMC) which is characterized by adaptively switching, for example, the QPSK modulation scheme and 16-level QAM scheme in accordance with the wireless environment between the base stations and mobile stations.
Moreover, the HSDPA employs the H-ARQ (Hybrid Automatic Repeat request) scheme. The H-ARQ is characterized by that the data is re-transmitted from a base station in response to a request from a mobile station and the mobile station performs the error correction decoding using both the already received data and received data re-transmitted when the mobile station has detected an error in the received data from the base station. As described above, in the H-ARQ scheme, the gain of error correction decoding can be increased and the number of times of re-transmission is controlled (reduced) by effectively utilizing the received data if an error is detected.
The main wireless channels used in the HSDPA include the HS-SCCH (High Speed Shared Control Channel), HS-PDSCH (High Speed Physical Downlink Shared Channel), and HS-DPCCH (High Speed Dedicated Physical Control Channel).
The HS-SCCH and HS-PDSCH are the shared channels in the downlink direction (namely, direction to the mobile station from the base station).
The HS-SCCH is the control channel for transmitting various parameters for the data to be transmitted by the HS-PDSCH. Various parameters include, for example, the modulation type information indicating the modulation scheme for transmitting the data with the HS-PDSCH, the number of assignment of spreading codes (number of spreading codes) and the information such as a rate matching pattern for the transmitting data.
However, the HS-SCCH is capable of simultaneously transmitting the control signal to a plurality of mobile stations utilizing a plurality of spreading codes (for example, four spreading codes) and the mobile station tries to perform the decoding (here, for example, the Viterbi decoding) to the signals obtained by despread with all (four) spreading codes. A plurality of HS-SCCHs used for simultaneous transmission with a plurality of spreading codes are called a set of HS-SCCHs.
The data destined to the own mobile station can be identified from that destined to the other mobile stations by judging the HS-SCCH addressed to the own station among a set of HS-SCCHs to have sufficient difference in the final pathmetric values. When the control signal is transmitted via the HS-SCCH to the same mobile station with the continuous sub-frame, it is preferable to transmit the data with the same HS-SCCH among a set of HS-SCCHs (namely, to transmit the data with the same spread code) in view of alleviating the processing load of the mobile station.
Accordingly, when only one HS-SCCH among a set of HS-SCCHs has once detected the data destined to the own station on the basis of the pathmetric value or the like in the Viterbi decoding as described above, it is enough for the next continuous HS-SCCH to perform the despreading using the identical spreading code in place of conducting the despreading using all of the four despreading codes.
When the mobile station has detected the data is not destined to the own station based on the HS-SCCH, the despreading must be performed again using all of the four despreading codes.
Meanwhile, the HS-DPCCH is the dedicated control channel in the uplink direction (namely, direction to the base station from the mobile station) and is used when the mobile station transmits respectively the ACK signal and NACK signal to the base station in accordance with acknowledgment and non-acknowledgment of reception of the data received via the HS-PDSCH. If the mobile station fails reception of data (when a CRC error is generated in the receiving data or the like), the base station executes the re-transmission control because the NACK signal is transmitted from the mobile station.
Moreover, the HS-DPCCH is also used by the mobile station which has measured (measured for example within the period of the former sub-frame) the reception quality (for example, SIR) of the receiving signal received via the CPICH from the base station to transmit the CQI (Channel Quality Indicator) to the base station in accordance with the result of measurement
The base station switches, when the wireless environment in the downlink direction is judged to be good based on the received CQI, the modulation scheme to the scheme which can transmit the data in the higher transmission rate. If the wireless environment is judged to be bad, on the contrary, the base station switches the modulation scheme to the scheme which can transmit the data in the lower transmission rate (namely, adaptive modulation is performed).
Channel Format
Next, a channel format in the HSDPA will be described below.
FIG. 1 is a diagram for illustrating a channel format in the HSDPA. Each channel is isolated with the spreading code because the W-CDMA adopts the code division multiple access scheme.
First, the channels not yet described will be explained briefly.
The CPICH (Common Pilot Channel) and P-CCPCH (Primary Common Control Physical Channel) are respectively common channels for the downlink direction and are also used in the ordinary communications in addition to the HSDPA.
The CPICH is the channel used in the mobile station for channel estimation, cell search and timing reference of the other downlink physical channel in the same cell. Namely, this CPICH is the channel for transmitting the pilot signal. The P-CCPCH is the channel for transmitting the broadcast information.
Next, the timing relationship of channels will be described with reference to FIG. 1.
As illustrated in the figure, each channel forms one frame (10 ms) with 15 slots. As described previously, since the CPICH is used as the reference of the other channels, the top of the frames of both P-CCPCH and HS-SCCH channels are matched with that of the frame of the CPICH channel. Here, the top of frame of the HS-PDSCH channel is delayed by two slots for the HS-SCCH or the like. It is necessary to perform the demodulation of the HS-PDSCH with the demodulation scheme corresponding to the modulation scheme received because the mobile station receives the modulation type information via the HS-SCCH channel. Moreover, the HS-SCCH and HS-PDSCH form one sub-frame with three slots.
The HS-DPCCH channel is not synchronized with the CPICH but it is the channel in the uplink direction and is based on the timing generated in the mobile station.
The channel format of the HSDPA has been described briefly above.
Next, contents and coding sequence of the data to be transmitted by the HS-SCCH channel will be described.
Data transmitted by the HS-SCCH
Following data can be transmitted with the HS-SCCH. Each data is mainly used for the reception process of the corresponding HS-PDSCH (delayed by two slots).
(1) Xccs (Channelization Code Set information)
(2) Xms (Modulation Scheme information)
(3) Xtbs (Transport Block Size information)
(4) Xhap (Hybrid ARQ Process information)
(5) Xrv (Redundancy and constellation Version)
(6) Xnd (New Data indicator)
(7) Xue (User Equipment identity)
Here, the Xccs of item (1) is the data indicating the spreading code used for transmission of the data through the HS-PDSCH (for example, data indicating the combination of the number of multi-codes and code offset) and is formed of 7 bits.
Moreover, the case where the spreading factor (SF) is 16 is considered here for more practical description.
When SF is 16, the spreading code of 16 kinds may be used. However, since the 0th spreading code is used for transmission of the broadcast information, the 1st to 15th codes may be used for the HS-PDSCH. Since the spreading codes used for transmission of the HS-PDSCH are used continuously (for example spreading code O, O+1, . . . , O+P−1), it is enough when O and P are transmitted after these are coded and converted into 7 bits under the condition that the top spreading code used is defined as O and the number of spreading codes used is defined as P.
Therefore, following coding method is thought as an example of the coding method.                1st to 3rd bits (code group indicator)                    min (P−1, 15−P)                        4th to 7th bits (code offset indicator)                    |O−1−┌P/8┘×15|                        
Here, min (A, B) indicates a smaller one of A and B, while ┌N┘ indicates the maximum integer not exceeding N.
The data of 7 bits of Xccs has been defined above and the correspondence thereof is indicated in FIG. 2. According to FIG. 2, for example, it can be understood easily that when the data of Xccs corresponding to the case where P=5 and O=6 becomes “1000101” and the data of Xccs corresponding to the case where P=9 and O=2 becomes “1101110”.
Xms of item (2) is the data indicating that the modulation scheme used for the HS-PDSCH is any one of the QPSK and 16-level QAM and is formed of one bit.
Xtbs of item (3) is the data used for calculation of the transport block size (data size transmitted by one sub-frame of the HS-PDSCH) of the data transmitted by the HS-PDSCH and is formed of six bits.
Xhap of item (4) is the data indicating the process number of the H-ARQ and is formed of three bits. The base station cannot judge acknowledgment or non-acknowledgement of the reception of data transmitted first in the mobile station until the ACK and NACK are received. However, since the transmission efficiency is lowered when the next new data is not transmitted until the reception of these data, the next new data is transmitted before reception of the ACK and NACK signals. While, since the H-ARQ is employed in the mobile station, when the re-transmission is performed, it must be recognized that with which data already received the data re-transmitted must be combined.
Therefore, before the transmission of each data via the HS-PDSCH the base station notifies the process number of the data to the mobile station. Then the mobile station identifies the data flow received via the HS-PDSCH by the process number and judges whether the mobile station combines the receiving data with the already received data, wherein the receiving data and the already received data belong to same flow (namely corresponding to same process number).
Xrv of item (5) is the data indicating a rate matching pattern and a kind of constellation re-arrangement in the re-transmission of the HS-PDSCH and is formed of three bits.
Xnd of item (6) is the data indicating whether the transmission block of the HS-PDSCH is the new block or re-transmission block and is formed of one bit.
Xue of item (7) is the data indicating the mobile station discriminating information and is formed of 16 bits.
Coding of data transmitted by HS-SCCH
FIG. 3 illustrates the coding sequence of each data (coding apparatus) of the items (1) to (7) transmitted by the HS-SCCH. The coding sequence is mainly executed in the base station.
In FIG. 3, the reference numeral 1 designates a coding unit; 2, a rate matching process unit; 3, a multiplier; 4, a CRC arithmetic unit; 5, a multiplier; 6, a coding unit; 7, a rate matching process unit; 8, coding unit; 9, a rate matching process unit.
Operations of each block will be described.
The Xccs (x1,1 to x1,7) (1) expressed with seven bits and Xms (x1,8) (2) expressed one bit are inputted to the coding unit 1 as the data in total of eight bits. Here, the former number of the subscripts means that it refers to the data to be transmitted with the first slot and the latter number partitioned by the comma (,) indicates the bit number.
The coding unit 1 adds the tail bits of eight bits to the input data and performs the convolutional coding process of the coding rate of 1/3 to the 16 bits in total. Therefore, the coded data becomes 48 bits in total and are given to the rate matching process unit 2 as z1,8 to z1, 48. The rate matching process unit 2 outputs the predetermined bits after adjustment to the number of bits (40 bits, in this case) accommodated within the first slot by performing the puncture and repetition process or the like (r1,1 to r4,40).
The data from the rate matching process unit 2 is multiplied with c1 to c40 with the multiplier 3 and are outputted as s1,1 to s1,40 and are then transmitted by the first slot (first part) as the top slot of one sub-frame in the HS-SCCH of FIG. 1.
Here, c1 to c40 have been obtained by moreover conducting bit adjustment similar to that in the rate matching process unit 2 with the rate matching process unit 9 to the b1 to b48 which has been obtained by the convolutional coding in the coding rate of 1/2, after addition of the tail bits of eight bits, of the data from the Xue (7) (Xue 1 to Xue 16) in the coding unit 8.
Meanwhile, the Xtbs (3)(x2,1 to x2,6) of six bits, Xhap (4) (x2,7 to x2,9) of three bits, Xrv (5) (x2,10 to x2,12) of three bits, Xnd (1) (x2,13) of one bit are inputted as y2,1 to y2,13 in total of thirteen bits to the coding unit 6 and moreover inputted thereto as y2,1 to y2,29 in total of 29 bits with addition of y2,14 to y2,29 of 16 bits.
Here, y2,14 to y2,29 have been obtained by conducting the CRC arithmetic process in the CRC arithmetic unit 4 to the total of 21 bits of (1) to (6) and then multiplying Xue (7)(Xue 1 to Xue 16) as the result of arithmetic operation.
The data y2,1 to y2,29 inputted to the coding unit 6 are inputted, after addition of the tail bits of 8 bits, to the rate matching process unit 7 as the data of 111 bits of z2,1 to z2,111 through the convolutional coding with the coding rate of 1/3.
The rate matching process unit 7 outputs the 80 bits of r2,1 to r2,80 with the process such as puncture process described above and these data r2,1 to r2,80 are transmitted with the 2nd and 3rd slots (second part) in one sub-frame in the HS-SCCH of FIG. 1.
As described above, the data are separately transmitted with individual slots, for example, the data of (1) and (2) with the first slot, while the data of (3) to (6) with the second and third slots. However, these are subjected in common to the CRC arithmetic operation and transmitted as the result of CRC arithmetic operation within the second slot. Accordingly, a reception error can be detected by perfectly receiving both first and second slots.
Moreover, since the data transmitted with the first slot is multiplied with Xue (7) with the multiplier 3 after the convolutional coding by the coding unit 1, when the data addressed to the other station is received with the first slot, difference in the final pathmetric values becomes small and it is proved that such data is never addressed to the own station with considerable possibility.
Contents in relation to the HSDPA described above are disclosed, for example, in 3rd generation Partnership Project: Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (3G TS 25.212) and 3rd generation Partnership Project: Technical Specification Group Radio Access Network; Physical layer procedures (FDD) (3G TS 25.214).
According to the background described above, a mobile station receives the first, second, and third slots of the HS-SCCH received from the base station and also receives, when there is no error in the result of CRC arithmetic operation, the data of HS-PDSCH which is received after the delay of two slots for the HS-SCCH.
However, acquisition of the result of CRC arithmetic operation requires total reception of HS-SCCH formed of three slots and results in a problem that a certain time is required until the result can be obtained.
Therefore, it is considered here to detect a reception error, for example, because a difference in the pathmetric values is small, by performing the Viterbi decoding or the like. However, setting of threshold to define such difference level is rather difficult. When the threshold is set to the lower level, decision in the earlier stage of reception error becomes considerably difficult because decision is made almost depending on the result of CRC arithmetic operation.
Therefore, one of the objects of the present invention is to detect the reception error of the HS-SCCH in the earlier stage or with higher accuracy.
Moreover, as described above, when the data is transmitted with the same HS-SCCH among the set of HS-SCCHs (namely, transmitted with the same spreading code) in view of alleviating the load of process of the mobile station, if any HS-SCCH among the set thereof is decided to be addressed to the own station incorrectly, the despreading is conducted with the spreading code for the same HS-SCCH for the sub-frame of the next HS-SCCH for which the result is continuous. Accordingly, the reception of the continuous HS-SCCH becomes difficult because of spreading of decision error of the HS-SCCH. Therefore, it is essential, from such point of view, to consider the enhancement in the receiving accuracy of the HS-SCCH as the object of the present invention.
While it is detected that the HS-SCCH is not addressed to the own station, it is required to conduct the despread using all of four despreading codes.
In addition to the object described above, it is also considered as the object of the present invention to provide the effect which can be attained with each structure described in the preferred embodiments of the present invention and cannot be realized with the prior art.